1. Technical Field
The present invention relates to a sheet post-processing apparatus and an image forming system including the sheet post-processing apparatus.
2. Description of the Related Art
Sheet post-processing apparatuses have been known which have functions of performing post-processing, such as curl correction, humidification, sheet folding, stapling, and punching, on sheets on which images are formed by image forming apparatus main bodies. Such sheet post-processing apparatuses may be required to reverse front and back sides of sheets subjected to the post-processing and discharge the sheets to the outside in some cases. As an apparatus for reversing front and back sides of a sheet, for example, a sheet reversing device described in Japanese Unexamined Publication No. 2002-160861 is known. However, if the sheet reversing device according to Japanese Unexamined Publication No. 2002-160861 is installed as it is in a sheet post-processing apparatus, the sheet post-processing apparatus is enlarged, and a sheet processing speed may be lowered.
In this connection, Japanese Unexamined Publication No. 8-169626 discloses a technique for reversing front and back sides of a sheet in a sheet post-processing apparatus in which the sheet is partially and temporarily discharged from a route for discharging the sheet to a sheet discharge tray, then pulled back to reverse the front and back sides of the sheet, and conveyed. Therefore, when the technique according to Japanese Unexamined Publication No. 8-169626 is used in the sheet post-processing apparatus, front and back sides of a sheet can be reversed and the sheet can be discharged to the outside without causing enlargement of the apparatus.
However, the technique according to Japanese Unexamined Publication No. 8-169626 has a risk that a user may mistakenly take out the sheet temporarily discharged on the sheet tray. In addition, when a corrugation roller is used to stiffen a sheet, there is a risk that the sheet is wrinkled when being discharged and pulled back. Further, there is a risk that positions of sheets stacked on the sheet discharge tray in an aligned state may be disordered. Furthermore, there is a risk that when a sheet is discharged and pulled back at a high speed, a part of the sheet discharged to a sheet discharge port may be curled up by receiving air resistance or wrinkled when being pulled back.
The present invention is made in view of the above-mentioned problems. One of the objects of the present invention is to provide a sheet post-processing apparatus capable of discharging a sheet by stably reversing front and back sides thereof without causing enlargement of the apparatus and a decrease in productivity.